Can anyone share some code for that kind of list box ? I do not want to use Smart GWT at the moment.

Another cool idea would be to add a small button on the right of a textbox and when the user clicks on that small button,
a pop up opens and the user can select values from that popup by checking them (checkboxes) and that would automatically
populates the textbox (values separated by commas) when he closes the popup.

How do i implement such widget ?
I am looking for samples, ideas, suggestions ...